Transmission method, transmitter, and receiver for multi antenna wireless communication system

ABSTRACT

A transmitter includes first generator to generate pilot source signal by modulating pilot sequence, second generator to generate data source signal with time length longer than that of pilot source signal by modulating data sequence, first cyclic shifter to perform cyclic shift of first shift amount to pilot source signal to generate first pilot signal, second cyclic shifter to performs cyclic shift of second shift amount to data source signal to generate first data signal, third cyclic shifter to perform cyclic shift of third shift amount to pilot source signal to generate second pilot signal, fourth cyclic shifter to perform cyclic shift of fourth shift amount to data source signal to generate second data signal, first transmit antenna to transmit first pilot signal and first data signal, and second transmit antenna to transmit second pilot signal and second data signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 13/336,289 filedDec. 23, 2011, which is a Continuation of U.S. application Ser. No.11/838,255, filed Aug. 14, 2007, which is a Continuation Application ofPCT Application No. PCT/JP2007/061506, filed May 31, 2007, which waspublished under PCT Article 21(2) in English.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2006-221029, filed Aug. 14, 2006.The entire contents of U.S. application Ser. No. 13/336,289, U.S.application Ser. No. 11/838,255, and Japanese Patent Application No.2006-221029 are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission method, a transmitterand a receiver for a multi antenna wireless communication system usingcyclic delay diversity.

2. Description of the Related Art

Transmit antenna diversity that is one of transmit diversity techniquesfor wireless communication transmits the same signals from a pluralityof antennas. As for the transmit antenna diversity, space time blockcoding (STBC) which makes transmission data blocks, operates its code,and changes the transmission order then transmits data; and cyclic delaydiversity (CDD) which simultaneously transmits signals subjected tocyclic shift for blocks have been well known.

In the CCD, as described, for example, in G. Bauch and J. S. Malik,“Parameter optimization, interleaving and multiple access in OFDM withcyclic delay diversity,” VTC-2004 spring, Vol. 1, pp. 505-509 (2004)(hereinafter, referred to as Document 1), a transmitter transmits datasignal from one antenna, and also it transmits the same data signal withthe cyclic shift performed thereto from other antennas. In a receiver,the data signals transmitted from each antenna of the transmitter aremixed and received.

Cyclic-shifted signals have high velocity phase rotation in frequencydomain. Therefore, mixing the cyclic-shifted signals with the notcyclic-shifted signals makes frequencies intensifying the signalsmutually and frequencies weakening the signals mutually on a frequencydomain at short frequency intervals. Thereby, the CCD eliminates burstpower drop in the frequency directions. Therefore, if error correctioncoding has been implemented as well as transmission data has fullyinterleaved in the frequency directions, the CCD may fully exert errorcorrection ability in the receiver, and may expect improving receptionperformance.

In the technique in the Document 1, the CCD requires an amplitudereference and phase reference for demodulating a spectrum varying with ahigh velocity in the frequency domain in order to demodulate receivedsignals. The transmitter has to transmit pilot signals defied in asystem to estimate channels from a plurality of antennas prior to thedata signals.

Each pilot signal being a redundant signal not directly contributing toa data transmission, the use of the pilot signals with long time lengthscauses a reduction in transmission efficiency of data. Therefore, ashort pilot signal length (time length) is desired. However, althoughthe Document 1 refers to a cyclic shift amount of the data signal, itdoes not refer to a cyclic shift amount of the pilot signal and thepilot signal length.

The object of the present invention is to shorten a pilot signal lengthas much as possible while enjoying an effect of the CDD to improve thedata transmission efficiency.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, a transmittercomprising: a first generator which generates a pilot source signal bymodulating a pilot sequence; a second generator which generates a datasource signal with a time length longer than that of the pilot sourcesignal by modulating a data sequence; a first cyclic shifter whichperforms a cyclic shift of a first shift amount to the pilot sourcesignal to generate a first pilot signal; a second cyclic shifter whichperforms a cyclic shift of a second shift amount to the data sourcesignal to generate a first data signal; a third cyclic shifter whichperforms a cyclic shift of a third shift amount to the pilot sourcesignal to generate a second pilot signal; a fourth cyclic shifter whichperforms a cyclic shift of a fourth shift amount to the data sourcesignal to generate a second data signal; a first transmit antenna whichtransmits the first pilot signal and the first data signal; and a secondtransmit antenna which transmits the second pilot signal and the seconddata signal is provided.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an exemplary block diagram depicting a wireless communicationsystem according to one embodiment;

FIG. 2 is another exemplary block diagram depicting the wirelesscommunication system according to the embodiment;

FIG. 3 is an exemplary schematic view depicting a transmit signal formatin the embodiment;

FIG. 4A is an exemplary schematic view depicting a pilot signal of aconstant amplitude and zero auto correction (CAZAC) sequence in theembodiment;

FIG. 4B is an exemplary schematic view depicting a cyclic-shifted pilotsignal on the basis of the pilot signal in FIG. 4A;

FIG. 5 is an exemplary view depicting a transmit signal generationprocedure in the embodiment;

FIG. 6 is an exemplary view depicting a receiving process in theembodiment;

FIG. 7 is an exemplary view depicting the detail of the receivingprocess in the embodiment;

FIG. 8 is an exemplary block diagram depicting a transmitter accordingto the embodiment;

FIG. 9 is an exemplary block diagram depicting a receiver according tothe embodiment;

FIG. 10 is an exemplary block diagram depicting a specific example of apart of the receiver;

FIG. 11 is an exemplary block diagram depicting another specific exampleof the part of the receiver;

FIG. 12 is an exemplary view depicting the detail of an operation of thereceiver;

FIG. 13 is an exemplary block diagram depicting other specific exampleof the part of the receiver;

FIG. 14 is an exemplary schematic view depicting a frame structure of atransmit signal;

FIG. 15 is an exemplary block diagram depicting a specific example of apart of the transmitter;

FIG. 16 is an exemplary block diagram depicting another specific exampleof the part of the transmitter;

FIG. 17 is an exemplary view depicting a transmit signal generationprocedure in other embodiment; and

FIG. 18 is an exemplary block diagram depicting a transmitter accordingto other embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

(Wireless Communication System)

A wireless communication system regarding one example of the inventionwill be set forth by referring to FIG. 1. A transmitter 1 has a firsttransmit antenna 2, and a second transmit antenna 3. A receiver 7 has areceive antenna 6. A system in FIG. 1 is typically used for a cellularcommunication system, but it is not limited to such a system. It is alsopossible for the system in FIG. 1 to be applied to a wireless LAN, afixed wireless access network, etc.

The transmitter 1 has a function to modulate user data to convert itinto a radio frequency (RF) signal in order to transmit the user data tothe receiver 7 wirelessly. The transmitter 1 performs transmit diversityby transmitting the RF signal from both the first and second transmitantennas 2 and 3.

The RF signal transmitted from the first and the second transmitantennas 2 and 3 arrives at the receive antenna 6 of the receiver 7through first and second channels (propagation paths) 4 and 5. If boththe first and second channels 4 and 5 are multipath channels, a maximumdelay time (maximum transmission delay time) from the path though whichthe first signal achieves the receive antenna 6 up to the path throughwhich the last signal achieves there is presumed within T₃.

The receive antenna 6 receives a signal in which the signal transmittedfrom the first transmit antenna 2 and the signal transmitted from thesecond transmit antenna 3 are mixed. The receiver 7 performs ademodulation process to the received signal from the receive antenna 6to reproduce the user data.

FIG. 2 illustrates another wireless communication system regarding theembodiment of the invention. In FIG. 1, the transmitter being presentonly one set, the system in FIG. 2 includes a plurality of transmitters,for instance, a first transmitter 1A and a second transmitter 1B. It issupposed that, in general, different users use each transmitter 1A and1B, which transmits different user data, respectively. Each transmitter1A and 1B have first transmit antennas 2A and 2B, and second transmitantennas 3A and 3B, respectively. The signals transmitted from theantennas 2A and 3A of the first transmitter 1A arrive at the receiveantenna 6 passing through the first and the second channels 4 and 5,respectively. The signals transmitted from the antennas 2B and 3B of thesecond transmitter 1B arrive at the receive antenna 6 passing through athird and a fourth channels (propagation paths) 8 and 9, respectively.It is assumed that the maximum transmission delay time of the channels4, 5, 8 and 9 is T₃.

The receiver 7 has to separate the signals transmitted from the firstand the second transmitters 1A and 1B. Therefore, in this embodiment,the data signals transmitted from the first and the second transmitters1A and 1B are transmitted though different frequencies, respectively.That is, it is presumed that frequency division multiplexing (FDM) isperformed. In this case, it may be supposed for the demodulation withina frequency band through which the data signals of one user istransmitted to be conducted a process similar to that of the systemconfiguration shown in FIG. 1.

(Transmit Signal Format)

FIG. 3 illustrates a format of a transmit signal transmitted from atransmitter. The transmit signal has a form of a single carrier signal,namely, a form in which transmission symbols generated by the modulationof the data signals are made a line linearly in a time direction. Onesignal block is constituted with a consecutive plurality of transmissionsymbols; a signal of a time T_(CP) equivalent to an end of a certainsignal block is copied and connected to a head of the signal block. Inan example in FIG. 3, the one signal block length is a time T and Mpieces of modulated symbols are arranged. A part added to the head isgenerally called a cyclic prefix (hereinafter referred to CP) and addedso as to enable frequency domain equalization in the receiver.

The signals transmitted from the transmitter are mainly classified intotwo types. One is a pilot signal used so that the receiver predictsconditions in the channels. The other is a data signal made bymodulating the user data. Each signal is presumed to each occupy oneblock, and it is supposed that the pilot signal and the data signal forone receiver are transmitted with time division multiplexing (TDM)implemented. However, it is not limited to the TDM; for instance, codedivision multiplexing (CDM) and FDM are also applicable to the presentembodiment.

The receiver extracts a section of the time T from the one signal blockto be received, and converts the extracted signal into a signal in afrequency domain through fast Fourier transform (FFT), etc. A startpoint of the section to be extracted is selected from a CP. Setting thesection to be extracted to the latter position of the CP enables toprevent the mixture of delayed waves of the precedent signal block. Inaddition to this, the CP having been cyclically added to the originalmodulated signal, the extracted signal of the time T is also assured itscontinuity at both ends.

For the pilot signal, for instance, a sequence called a constantamplitude and zero auto correction (CAZAC) sequence is utilized. TheCAZAC sequence has a constant envelope, and is a sequence further havinga character of which the autocorrelation value becomes “0” other that ata delayed time “0”, that is, a sequence having a completeautocorrelation property. The CAZAC sequence having the constantenvelope, it may reduce back off to prevent distortion of a transmissionamplifier, etc. Depending on the perfect autocorrelation property of theCAZAC sequence, code multiplexing by using the CAZAC sequence which hascyclically sifted in terms of time is available.

In the embodiment, the data signals having been subjected to the FDM, asto the pilot signal, the cyclic shift of the CAZAC sequence generatessignals orthogonal among users to achieve code multiplexing among theusers. That is to say, the system in the embodiment generates a pilotsignal A in a certain CAZAC sequence shown in FIG. 4A, and a pilotsignal B which is made by cyclically shifting the pilot signal A by timeT₃ and shown in FIG. 4B. Transmission block generation by adding the CPis omitted in FIGS. 4A and 4B.

The pilot signals A and B are mutually orthogonal due to the property ofthe CAZAC sequence. The maximum propagation delay time of the channelsare within the time T₃, two sets of transmitters transmit the pilotsignals A and B, respectively, even if the maximum delayed waves havearrived at the receiver, the delayed wave of the pilot signal A does notoverlap on a faster-most arrival wave of the pilot signal B. FIGS. 4Aand 4B having illustrated only two sequences as examples, generatingsequences by sifting the pilot signal A by 2T₃, 3T₃, 4T₃, . . . , thesystem can generate a plurality of sequences until the cyclic shift willmake a round.

(Generation Procedure of Transmit Signal)

A generation procedure of a transmit signal in the present embodimentwill be described in detail with reference to FIG. 5. The transmitsignal includes pilot signals to measure impulse responses (or frequencycharacteristics) of the first and the second channels and data signalwhich has mad by modulating the user data.

The pilot signals are generated by modulating a pilot sequence 13 thatis a CAZAC sequence of A bit. A modulation scheme is desirable to bepreset between the transmitter and receiver, for example, binarymodulation, such as binary phase shift keying (BPSK) or amplitude shiftkeying (ASK) are used appropriately. With modulation, the pilot sequenceis converted into a pilot source signal 15. A time length of the pilotsource signal 15 is T₁. If it is presumed that L symbols are generatedby modulation, for instance, in the case of implementation of BPSKmodulation, L equals to A.

The cyclic shift and CP addition are performed to the pilot sourcesignal 15. It is supposed that the way of being performed the cyclicshifts, especially, cyclic shift amounts varied depending on thetransmit antennas. The signal transmitted from the first transmitantenna is subjected to the cyclic shift by k₁ symbol or time T₁equivalent to the k₁ symbol. The cyclic shift is the same process as acyclic replacement. That is, the cyclic shift is a replacement processnot varying an information amount to be transmitted by shifting the partwhich has become longer than the source signal due to a delay processingas well as adding a delay to the signal. After performing the cyclicshift like this manner, the CP is added in a method shown in FIG. 3.

A cyclic shift with different time from that of the signal transmittedfrom the first transmit antenna is given to the pilot signal transmittedfrom the second transmit antenna. It is presumed that the cyclic shiftamount of the pilot signal transmitted from the second transmit antennais equal to a k₃ symbol, or a time τ₃ equivalent to the k₃ symbol. Afterthe cyclic shift, the CP is added. The cyclic-shifted pilot signaltransmitted from the first transmit antenna is referred to as a firstpilot signal, and the cyclic-shifted pilot signal transmitted from thesecond transmit antenna is referred to as a second pilot signal. Thefirst and the second pilot signals are transmitted from each antennasimultaneously.

Next, a generation procedure of the data signal will be described. Thetransmitter generates user data 11 of J bit. Performance of errorcorrection coding (ECC) to the user data 11 generates a data sequence 12of B bit. Further, the system modulates the data sequence 12 to generatea data source signal 14 with M pieces of symbols and with time lengthT₂. For the modulation here, for instance, a modulation scheme, such asa BPSK, quadrature amplitude modulation (QPSK), 16 QAM, and 64 QAM isusable. It is supposed that the modulation scheme used here has beenpreset between the transmitter and receiver, or notified from thetransmitter to the receiver in another method.

As like the pilot signal, two types of cyclic shifts differing in shiftamount are performed to the data source signal 14. A first data signal16 transmitted from the first transmit antenna is a signal in which acyclic shift is performed to the data source signal 14 by k₂ symbol, orby time₂ equivalent to the k₂ symbol, and the CP is further added.

Similarly, a second data signal 17 transmitted from the second transmitantenna is a signal made by performing a cyclic shift to the data sourcesignal 14 by k₄ symbol, or by time τ₄ equivalent to the k₄ symbol, andby further adding the CP. The first and the second data signals 16 and17 are transmitted simultaneously from each transmit antenna.

In this embodiment, not to lose generality, it is assumed that τ₁<τ₃,and τ₂<τ₄. Here, making difference between the difference τ₃−τ₁ of thecyclic shift amounts between the first pilot signal and the second pilotsignal from the difference τ₄−τ₂ of the cyclic shift amounts between thefirst pilot signal and the second pilot signal produces the followingadvantages.

In the cyclic shift, if the shift amount exceeds a transmission blocklength, the signal being shifted more than one round; it is a possiblerisk for the shift amount becomes the same sequence as a sequence with alength shorter than the transmission block length. Accordingly, thecyclic shift amounts of the first and the second pilot signals 17 and 19are smaller than T₁, and the cyclic sift amounts of the first and thesecond data signals 16 and 18 have to set smaller than T₂. Thisexpresses at the same time that the difference τ₃−τ₁ has to be smallerthan T₁, and the difference τ₄−τ₂ has to be smaller than T₂.

Here, if the difference τ₃−τ₁ equals to the difference τ₄−τ₂, the timelength T₁ and T₂ inevitably has to be larger than both the differenceτ₃−τ₁ and the difference τ₄−τ₂. Then, for instance, the case, in whichthe system cannot always satisfy the desire to make the time length T₁of the first and the second pilot signals 17 and 19 smaller than thetime length T₂ of the first and the second data signals 16 and 18,occurs. More specifically, it is impossible to make the time length T₁of the first and the second pilot signals 17 and 19 smaller than thedifference τ₄−τ₂ of the first and the second data signals 16 and 18. Thepilot signals are redundant signals not contributing directly to thetransmission of the user data. Therefore, if the system cannot shortenthe pilot signal lengths, the case of excess transmissions of theredundant signals occurs, and the system has to further shorten the datasignal lengths and poses the reduction in transmission rate, orsaturation at a slow transmission rate.

Here, like the embodiment, if it is assumed that the difference τ₃−τ₁and the difference τ₄−τ₂ are different from each other, or they are setseparately, the time length T₁ is enough to be the difference τ₃−τ₁ ormore, and the time length T₂ is enough to be the difference τ₄−τ₂ ormore. Then, the time length T₁ is not restricted by the value of thedifference τ₄−τ₂, the pilot signal lengths become possible to be setshorter. Accordingly, the system decreases its redundancy, increases theuser data amount which can transmit of the reduction due to thedecrease, and results in improving the transmission rate.

Further, in the embodiment, when the difference τ₄−τ₂ equals to the timelength T₂/2, the effect of the CDD becomes maximum. Here, if thedifference τ₃−τ₁ equals to the difference τ₄−τ₂, the time length T₁ hasto be set larger than the time length T₂/2. Strictly speaking, thedelayed waves of maximum time length T₃ are occurred in the channels, sothat the time length T1 has to be set longer than the time length inwhich the time length T3 is added to the time length T₂/2. However,according to the embodiment, if the difference τ₃−τ₁ is set smaller thanthe time length subtracting T₃ from T₂/2, the time length T₁ may bewithin a range larger than the difference τ₃−τ₁. For example, if T₁=T₂/2is satisfied, the time length T₁ of the pilot source signal 15 becomes ahalf of the time length T₂ of the data source signal 14. Thereby, thesystem easily performs memory management of the transmitter, further,the system becomes possible to have an advantage on mounting, becausethe FFT for the frequency compensation in the receiver. At this time,the effect of the CDD is not spoiled.

(Reception Method)

Outline of a reception operation in the present embodiment will beexplained by referring to FIG. 6. The first transmit antenna 2 of thetransmitter 1 transmits the first pilot signal 17 cyclic-shifted by thetime τ_(t) and the first data signal 16 cyclic-shifted by the time τ₂following the time τ₁. At the same time, the second antenna 3 transmitsthe second pilot signal 19 cyclically shifted by the time τ₃, and thesecond data signal 18 cyclically shifted by the time τ₄.

The signals transmitted from the first and the second transmit antennas2 and 3 are mixed and received at the receive antenna 6 through thefirst channel 4 and the second channel 5 with the maximum delay time T₃.The pilot signals are those in the CAZAC sequence, by obtaining acorrelation to the pilot source signal 15 for the first and the secondpilot signals 17 and 19 mixed at the receive antenna, the system canobtain impulse responses of the first and the second channels 4 and 5.

The impulse response of the first channel 4 is referred to as a firstimpulse response, and the impulse response of the second channel 5 isreferred to as a second impulse response. In FIG. 6, examples of eachshape of the first and the second impulse responses are shown,respectively. It is thought to equalize the signal in which the firstand second data signals 16 and 18 transmitted from the first and secondtransmit antennas 2 and 3 are mixed, namely, to compensate itsdistortion by using these impulse responses. To equalize the mixed datasignals, it is necessary to obtain the impulse response mixed aftersifting by the same amount of that of the data signals. A generationmethod of the impulse responses will be described by referring to FIG.7.

To generate the impulse response to equalize the signals made by mixingthe first and second data signals 16 and 18, the system rearrange thefirst and second impulse responses in the section of the time T₂.

If the first arrival time of the first data signal is set to t₂, thefirst impulse response is arranged at a position away by the time τ₂from the time t₂. The second impulse response is arranged at a positionaway by the time τ₄ from the time t₂. The foregoing rearrangementprocess is called a profile adjustment. The system can obtain theimpulse response having the same shift amount as that of the data signalby the profile adjustment, and it can use the impulse response tocompensate the distortion of the received data signal.

(Transmitter)

The transmitter regarding the present invention will be described byreferring to FIG. 8. The transmitter in FIG. 8 comprises a pilotsequence generator 103, a pilot sequence modulator 105, a user datagenerator 101, an error correction coding unit 102, a data sequencemodulator 104, first to fourth cyclic shifters 106-109, a sift amountcontroller 110, first to fourth CP adders 111-114, a transmit signalselecting unit 117, first and second selectors 115 and 116, analogtransmitter units 118 and 119, and first and second transmit antennas121 and 122.

The pilot sequence generator 103 generates a pilot sequence presetbetween the transmitter and receiver. In the embodiment, the pilotsequence is presumed as the CAZAC sequence. The generated pilot sequenceis supplied to the pilot sequence modulator 105.

The pilot sequence modulator 105 performs prescribed modulation to thepilot sequence generated from the sequence generator 103 to generate thepilot source signal 15. The generated pilot source signal 15 is suppliedto the first cyclic shifter 106 and the third cyclic shifter 108.

The user data generator 101 generates the user data to be transmitted tothe receiver 7. The user data generated from the user data generator 101is supplied to the coding unit 102. The coding unit 102 performs errorcorrection coding to the user data obtained from the generator 101. Thecoding may use, for instance, convolution coding, turbo coding, etc. Theencoded data is a data sequence 12 shown in FIG. 2, and it is suppliedto the data sequence modulator 104 so as to be modulated.

The data sequence modulator 104 modulates the data sequence from thecoding unit 102. As for a modulation scheme, for example, the BPSK,QPSK, 16 QAM, or 64 QAM is usable. The modulation scheme used here issupposed to be shared between the transmitter 1 and receiver 7. Thegenerated signal is the data source signal 14 shown in FIG. 5, andapplied to the second cyclic shifter 107 and fourth cyclic shifter 109.

The first to fourth cyclic shifter 106-109 performs cyclic shifts to theinput pilot source signal 15 or data source signal 14. The cyclic shiftamount is given from the controller 110. The cyclic-shifted signals areapplied to the first to fourth CP adders 111-114.

The controller 110 sets cyclic shift amounts to the first to fourthcyclic shifters 106-109. More specifically, the controller 110 sets thecyclic shift amounts of each τ₁, τ₂, τ₃, and τ₄ to the first to fourthcyclic shifters 106-109, respectively. To obtain a maximum diversityeffect in the CDD, as examples for the setting of the times τ₁, and τ₂,it is preferable for τ₄−τ₂, to be a half of the block length T₂ of thedata signal. As an example for the setting of the τ₁, and τ₃, when aplurality of users transmit pilot signals simultaneously as shown inFIG. 2, the system sets so that the τ₁, and τ₃ do not become the samecyclic shift amounts of the other pilot signals.

The CP adders 111-114 add CPs to each signal cyclically shifted by thecyclic shifters 106-109. All operations of the first to fourth CP adders111-114 are identical, only their output destinations are different fromone another. Outputs from the first to fourth CP adders 111-114 areconnected to the first and second selectors 115 and 116, respectively.

The first selector 115 supplies either the first pilot signal obtainedfrom the first CP adder 111 or the first data signal obtained from thesecond CP adder to the succeeding first analog transmitter unit 118.Similarly, the second selector 116 supplies either the second pilotsignal obtained from the third CP adder 113 or the second data signalobtained from the fourth CP adder to the succeeding second analogtransmitter unit 119. The transmit signal selecting unit 117 instructseach selector 115 and 116 so as to decide which signal should be outputthe succeeding states.

The selecting unit 117 instructs the two selectors 115 and 116 eitherthe pilot signals or data signals should be applied to the analogtransmitter units 118 and 119. That is to say, it instructs so as toapply the pilot signals at the transmission times thereof, and apply thedata signals at the time transmission times of the data signals. Thefirst and second pilot signals 17 and 19 are sent simultaneously, andthe first and second data signals 16 and 18 are also sentsimultaneously. The pilot signals 17 and 19 and the data signals 16 and18 are transmitted at different times, respectively.

The analog transmitter units 118 and 119 convert the transmit signalsoutput from the selectors 115 and 116 into RF signals, respectively, andoutput them to the first and second transmit antennas 121 and 122,respectively. The first and the second transmit antennas 121 and 122transmit the RF signals output from the analog transmitter units 118 and119 to the channels.

(Receiver)

The receiver regarding the present embodiment will be explained withreference to FIG. 9. The receiver comprises a receive antenna 201, aanalog receiver unit 202, a reference single generator 205, a correlator206, a profile adjustment unit 207, a compensation signal generator 209,a synchronizer 204, a CP remover unit 203, FFT unit 208, a distortioncompensator 210, an IFFT unit 211, a data sequence demodulator 212, anda user data extractor 213.

The received pilot signal and the received data signal received by thereceive antenna 201 are forwarded to the following analog receiver unit202. The analog receiver unit 202 converts the received signal of aratio frequency into a baseband signal. The received signal convertedinto the baseband signal is forwarded to the CP remover unit 203,synchronizer 204 and correlator 206.

The synchronizer 204 obtains a CP position by mainly using the pilotsignal and supplies information on the CP position to the CP removerunit 203.

The reference signal generator 205 generates a reference signal to beused by the correlator 206. The reference signal is a signal tocalculate correlation between the reference signal and the receivedsignal by means of the correlator 206, and in the embodiment, it is apilot source signal cyclically shifted by the times τ₁, and τ₃, namely,the transmitted first and second pilot signals 16 and 18.

The correlator 206 performs correlation calculation between the pilotsignals (received pilot signals) during reception and the referencesignal generated from the generator 205 to obtain mutual correlationvalues. The correlation calculation process produces the aforementionedfirst and second impulse responses. The correlator 206 will be describedin detail below. The mutual correlation values calculated by thecorrelator 206 are supplied to the profile adjustment unit 207.

The profile adjustment unit 207 generates impulse responses forcompensation to compensate the distortion in the data signals inaccordance with the method described in FIG. 7 from the mutualcorrelation values obtained by the correlator 206, namely, from thefirst and second impulse responses. The generated impulse responses forcompensation are applied to the compensation signal generator 209.

The signal generator 209 converts the impulse responses obtained fromthe adjustment unit 207 into a compensation signal for a distortioncompensation process. In the embodiment, frequency domain equalizationbeing used, the compensation signal generation process becomes an FFTprocess. The compensation signal generated from the generator 209 isforwarded to the distortion compensator 210.

The CP remover unit 203 removes the CP from the received signal, andextracts a signal block therefrom to supplies it to the FFT unit 208.

The FFT unit 208 converts the signal block from which the CP is removedinto the signal in a frequency range to apply it to the distortioncompensator 210. The compensator 210 mainly compensates the distortionin the data signal due to the channel. That is, the compensator 210performs the distortion compensation by multiplying a reverse responseof the compensation impulse response to the data signal.

In the system using the CDD like this embodiment, the distortioncompensator 210 further treats a process to recover the delay due to thecyclic shift. To perform the distortion compensation, for instance, awell known algorithm, such as a zero forcing (ZF) method, a least square(LS) method, or a minimum mean square error (MMSE) method may beutilized.

In such a case, the system may recover the cyclic shift by performingthe distortion compensation though the use of the sum of the impulseresponses which have been cyclically shifted by the same cyclic shiftamount of the first and second data signals 16 and 18, namely, throughthe use of the compensation impulse response obtained by the profileadjustment unit 208.

The IFFT unit 211 converts the compensated spectrum output from thedistortion compensator 210 into the signal in the time range to supplyit to the data sequence demodulator 212. The demodulator 212 demodulatesthe data sequence by using the demodulation scheme which has decidedbetween the demodulator 212 and the transmitter 1. The demodulatedsignal is forwarded to the user data extractor 213. The extractor 213demodulates of error correction codes to the reception data sequenceobtained from the demodulator 212 to extract the user data 214.

Next, a concrete example of the reference signal generator 205,correlator 206, and profile adjustment unit 207 shown in FIG. 9 will begiven accounts by referring to FIG. 10.

The reference signal generator 205 generates the same signal as thefirst pilot signal generated on the transmitter side by a first pilotsignal generator 2051, and generates the same signal as the second pilotsignal generated on the transmitter side by a second pilot signalgenerator 2052. That is, the first pilot signal generator 2051 generatesa signal cyclically shifted the pilot source signal 15 by the time τ₁,and the second pilot signal generator 2052 generates a signal cyclicallyshifted the pilot source signal 15 by the time T₃.

The first and the second pilot signals generated from the signalgenerator 205 in this way are supplied to the correlator 206. Thecorrelator 206 has a first matched filter 2061 and a second matchedfilter 2062. By the first matched filter 2061 setting the first pilotsignals to a tap coefficient, a first mutual correlation value betweenthe first pilot signal and a pilot signal (received pilot signal) in areceived signal 221 is obtained. The first mutual correlation valuerepresents the first impulse response in the first channel. Similarly,by the second matched filter 2062 setting the second pilot signal as atap coefficient, a second mutual correlation value between the secondpilot signal and the received pilot signal is obtained. The secondmutual correlation value represents the second impulse response in thesecond channel.

Two output signals (mutual correlation values) from the correlator 206are input to the profile adjustment unit 207. The adjustment unit 207has a first delay unit 2071 and a second delay unit 2072. The firstdelay unit 2071 delays the output (first impulse response) from thefirst matched filter by τ₂−τ₁, and the second delay unit 2072 delays theoutput (second impulse response) from the second matched filter byτ₄−τ₃. The outputs from the delay units 2071 and 2072 are added by anadder 2073. That is, summing an impulse response for first compensationand an impulse response for second compensation produces an impulseresponse for third compensation 223 to compensate the data signal indistortion.

Next, another specific example of the reference signal generator 205,correlator 206 and profile adjustment unit 207 shown in FIG. 9 will beexplained with reference to FIG. 11.

Similar to the aforementioned example, the signal generator 205generating one sequence to be used by the correlator 206 to calculatethe mutual correlation value, the time length of the output signal hasbecome twice in comparison to the forgoing example. That is, the signalgenerator 205 outputs a pilot source signal repeatedly generated from apilot source signal generator 2053 twice through a repeater 2054.

In the correlator 206, the third matched filter 2063 produces a mutualcorrelation between the twice repeated signal of the pilot source signalgenerated from the signal generator 205 and the pilot signal in thereceived signal. The third matched filter 2063 has a tap twice as longerthan the pilot source signal and the tap coefficient becomes one made byrepetitions of two times of the pilot source signal.

The sequence in which the pilot source signal is cyclically shifted foran arbitrary time period may be assumed as a part of the signal in whichthe pilot source signal has been repeated twice. Therefore, if the pilotsignal is input to the third matched filter 2063 regardless of thecyclic shift amount, the mutual correlation value may be obtained.However, in comparison to the impulse response which occurs by inputtingthe pilot source signal without being applied the cyclic shift, if thepilot signal with being applied the cyclic shift by the time τ is input,the impulse response is also output with a delay by time τ.

Inputting received signal according to the embodiment to the correlator206 produces impulse responses like ones shown with dot lines in FIG.12. In other words, an impulse response in the first channel 4 throughwhich the impulse response is delayed by time τ₁, and an impulseresponse in the second channel 5 through which the impulse response isdelayed by time τ₃ are output for the time length T₁.

To utilize the output from the third matched filter 2063 to compensatethe distortion of the data signal, the profile adjustment unit 207performs adjustment. In the adjustment unit 207, the output from thethird matched filter 2063 is input to either a third delay unit 2076 ora fourth delay unit 2077 through a switch 2075. The switch 2075 iscontrolled by a switch controller 2074. The switch controller 2074applies a control signal to the switch 2075 so that the output from thethird matched filter 2063 is input to the third delay unit 2076 for thetime period from the time τ₁ to τ₁+T₃, and the output from the thirdmatched filter 2063 is input to the fourth delay unit 2077 for the timeperiod from the time τ₃ to τ₃+T₃.

The third delay unit 2076 and the fourth delay unit 2077 delay theinputs by τ₂−τ₁ and τ₄−τ₃, respectively. An adder 2078 adds the outputsfrom the third and the fourth delay units 2076 and 2077.

Such operations of the third and the fourth delay units 2076 and 2077,and the adder 2079 produce the impulse responses like ones indicatedwith dot lines in FIG. 12. In terms of the impulse responses obtainedlike this manner, the positions being equivalent to the cyclic siftamounts of the data signal, the impulse responses may be utilized forthe distortion compensation of the data signal.

FIG. 13 illustrates other concrete example of the adjustment unit 207.According to FIG. 13, the output signal 222 from the correlator 206 inFIG. 11 is converted from serial data to parallel data through aserial-parallel converter (S/P) 2081. The parameter output from the S/P2081 is stored in a memory 2082 once. On reading out data from thememory 2082, the order of the data is changed through a switch 2083, andalso a part of the data is output as “0”. This change in ordercorresponds to the operations of the third and the fourth delay units2076 and 2077 in FIG. 11 and acts to change the cyclic shift amounts. Anoutput signal from the switch 2083 is converted from parallel data toserial data through a parallel-serial converter (P/S) 2084. As a result,the impulse response for third compensation 223 is produced.

According to the concrete examples in FIG. 11 and FIG. 13, theconfigurations thereof are made simple in comparison with the concreteexample in FIG. 10. In the configuration of FIG. 10, the correlator 206should have a plurality of matched filters (in an example of FIG. 10,two matched filters 2061 and 2062). More specifically, in simultaneouslyreceiving a plurality of pilot signals differing in cyclic shift amount,matched filters with the same numbers as the types of the sift amountsare needed. In contrast, in FIG. 11, the length of the matched filterbecoming twice, only one matched filter (third matched filter 2063) ispossible to respond for any sift amount. Therefore, a circuit size ofthe receiver may be decreased, so that the consumption power inoperation may be reduced as well as the receiver is easily mounted.

(Frame Configuration)

FIG. 4 shows an example of a frame configuration in the embodiment. Aframe is 10 msec long, and divided into 20 pieces of sub frames. One subframe is 0.5 msec long. The sub frame is further divided into eightpieces of blocks (referred to as first to eighth transmission blocksfrom the top in time). CPs are added to each transmission block. Thesecond and the seventh transmission blocks are short blocks (SB) withhalf of time lengths each. Here, the time length does not include theCP. The first, the third to sixth, and eighth blocks are referred to aslong blocks (LBs), specifically, it is presumed that the LB has a lengthof 66.7 μsec, the SB has a length of 33.3 μsec, and the CP has a lengthof 4.13 μsec. It is supposed that the SB transits the pilot signal andthe LB transmits the data signal.

The first and the second transmit antennas transmit the sub framessimultaneously, but the cyclic shift amounts of each block differs fromone another between the sub frames transmitted from the both transmitantennas. Here, the difference includes the case in which one is notcyclically shifted and the other is cyclically shifted. For instance,each transmission block of the transmit signal from the first transmitantenna does not cyclically shift, and the transmit signal from thesecond transmit antenna cyclically shifts to halves of the LB and SB,namely, each transmission block cyclically shifts by 33.3 μsec and 16.7μsec for the LB and for the SB, respectively. Or, the LB of the transmitsignal from the first transmit antenna may be cyclically shifted by 16.7μsec, and the SB thereof from the second transmit antenna may becyclically shifted by 25 μsec.

(Specific Example of Data Sequence Modulation Unit and Pilot SequenceModulation Unit)

FIG. 15 and FIG. 16 show detailed configuration examples of the sequencemodulation unit to be used for the pilot sequence modulator 105 and thedata sequence modulator 104, respectively. In FIG. 15, the sequencemodulation unit converts an input signal 301 into a signal once in afrequency rang through a DFY unit 302, inputs it to an IFFT unit 303with an IFFT size larger than the DFT size, then, the modulation unitachieves frequency conversion. The IFFT size being larger than the DFTsize, the “0” is input to a part to which the output from the DFT unit302 among the inputs to the IFFT unit 303 is not connected.

In FIG. 16, the modulation unit uses the same DFT and IFFT as those ofFIG. 15, but the “0” are inserted into each frequency components in theoutput from the DFT unit 402 converting an input signal 401 into asignal in the frequency range, so that the output is input to an IFFTunit 403. According to FIG. 16, for instance, if the “0” are insertedinto every second output from the DFT unit 402, on the time axis, theinput signal 401 to the DFT unit 402 are frequency-converted and alsothe signal repeated twice is output from the IFFT unit 403.

Using a configuration, such as in FIG. 15 or FIG. 16, to the pilotsequence modulator 105 and to the data sequence modulator 104, a singlecarrier signal of an arbitrary frequency becomes possible to begenerated.

Other Embodiment

In succession, other embodiments will be set forth by referring to FIG.17 and FIG. 18. FIG. 17 shows generation procedures of transmit signalsin the other embodiment. In the aforementioned embodiment, as shown inFIG. 5, in generating the first pilot signal 17 and the first datasignal 16, CP addition and cyclic shifts are performed to the pilotsource signal 15 and the data source signal 14, respectively.

On the contrary, in FIG. 17, the embodiment does not conduct the cyclicshift, but generates the first pilot signal 17 and the first data signal16 by conducting the CP addition to each pilot source signal 15 and thedata source signal 14. That is, FIG. 17 shows an example in which thetime τ₁ and τ₂ are set to “0”.

In this case, like the foregoing embodiment, it is desirable that thecyclic shift amounts of the second pilot signal 19 and of the datasignal 18 be made different from each other, and also the cyclic shiftamount of the second pilot signal 19 is set smaller than time length T₁,and the cyclic shift amount of the second data signal is set smallerthan the time length T₂. Thereby, like the foregoing embodiment, itbecoming possible for the lengths of the pilot signals shorter, theredundant is decreased, and the transmission rate of the data signal isimproved.

Further, like the aforementioned embodiment, it is preferable that thetime length T₁ be a half of that of the time length T₂ or shorter andthe cyclic shift amount of the second data signal 18 be a half of thetime length T₂ or shorter.

FIG. 18 illustrates a transmitter in further other embodiment. FIG. 17differs from FIG. 8 in that the first cyclic shifter 106 and the secondcyclic shifter 107 in FIG. 8 are omitted, and the pilot source signalfrom the pilot sequence modulator 105 and the data source signal fromthe data sequence modulator 104 are directly input to the first CP adder111 and the second CP adder 112.

On the other hand, the receiver in this embodiment being basicallysimilar to that of in FIG. 6, the configuration of the profileadjustment unit 207 differs from that of the foregoing embodiment. Thatis, the profile adjustment unit 207 is provided with a cyclic shifter toconduct a cyclic shift of a cyclic shift amount which is made bysubtracting the cyclic amount of the second pilot signal from the cyclicamount of the second data signal in response to the second impulseresponse. The adjustment unit 207 sums the impulse response for secondcompensation and the first impulse response through the adder thenobtains the final impulse for third compensation to be used for thedistortion compensation of the data signal.

As mentioned above, according the embodiments, in a multi antennawireless communication system using the CDD, shortening the pilot signallength as much as possible while enjoying the effect of the CDD enablesimprovement of the transmission efficiency in data.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

The present invention is effective in a multi antenna wirelesscommunication system such as in mobile communication system.

What is claimed is:
 1. A transmitter comprising: a generator configuredto generate a first sequence, a second sequence, a first block signal,and a second block signal, the first sequence being the same as asequence obtained by performing a first cyclic shift on a CAZACsequence, an amount of the first cyclic shift being a first amount, thesecond sequence being the same as a sequence obtained by performing asecond cyclic shift on the CAZAC sequence, an amount of the secondcyclic shift being a second amount different from the first amount, thefirst block signal being the same as a signal obtained by performing athird cyclic shift on a block signal, an amount of the third cyclicshift being a third amount, the second block signal being the same as asignal obtained by performing a fourth cyclic shift on the block signalan amount of the fourth cyclic shift being a fourth amount differentfrom the third amount; wherein a period in which the first sequence andthe second sequence are transmitted differs from a period in which thefirst block signal and the second block signal are transmitted; a gapbetween the first amount and the second amount differs from a gapbetween the third amount and the fourth amount; the first sequence andthe first block signal are transmitted at least via a first antenna; andthe second sequence and the second block signal are transmitted at leastvia a second antenna.
 2. The transmitter according to claim 1, wherein afrequency with which the first block signal and the second block signalare transmitted is set for the transmitter.
 3. The transmitter accordingto claim 1, wherein the first sequence and the second sequence aregenerated by performing at least IFFT; and the first block signal andthe second block signal are generated by performing at least
 4. Thetransmitter according to claim 1, wherein the generator performs errorcorrection coding on data, and the block signal is generated from thedata.
 5. The transmitter according to claim 1, wherein the block signalis generated from data, the data is modulated by a modulation scheme,the modulation scheme corresponding to a demodulation scheme employed ina terminal to communicate with.
 6. The transmitter according to claim 1,wherein the generator add a cyclic prefix to the first sequence, thesecond sequence, the first block signal, and the second block signal. 7.The transmitter according to claim 1, wherein the first sequence, thesecond sequence, the first block signal, and the second block signal aresingle carrier signals.
 8. The transmitter according to claim 1, furthercomprising: a first transmission analog circuit coupled to the firstantenna; and a second transmission analog circuit coupled to the secondantenna, wherein the first transmission analog circuit converts, into afirst signal of a radio frequency, the first sequence and the firstblock signal, and outputs the first signal to the first antenna; and thesecond transmission analog circuit converts, into a second signal of aradio frequency, the second sequence and the second block signal, andoutputs the second signal to the second antenna.
 9. The transmitteraccording to claim 1, wherein the block signal is generated based on auser data.
 10. A communication apparatus for receiving signals from atransmitter, comprising: a receiver configured to receive a firstsequence, a second sequence, a first block signal, and a second blocksignal, the first sequence used for estimating a first channelcondition, the first sequence being the same as a sequence obtained byperforming a first cyclic shift on a CAZAC sequence, an amount of thefirst cyclic shift being a first amount, the second sequence used forestimating a second channel condition, the second sequence being thesame as a sequence obtained by performing a second cyclic shift on theCAZAC sequence, an amount of the second cyclic shift being a secondamount different from the first amount, the first block signal being thesame as a signal obtained by performing a third cyclic shift on a blocksignal generated from data, an amount of the third cyclic shift being athird amount, the second block signal being the same as a signalobtained by performing a fourth cyclic shift on the block signalgenerated from the data, an amount of the fourth cyclic shift being afourth amount different from the third amount, wherein the firstsequence, the second sequence, the first block signal, and the secondblock signal are received via a receiving antenna; a period in which thefirst sequence and the second sequence are received differs from aperiod in which the first block signal and the second block signal aretransmitted; and a gap between the first amount and the second amountdiffers from a gap between the third amount and the fourth amount. 11.The communication apparatus according to claim 10, wherein a frequencywith which the first block signal and the second block signal arereceived is set for the transmitter;
 12. The communication apparatusaccording to claim 10, wherein the first sequence and the first blocksignal are transmitted at least via a first antenna of the transmitter;and the second sequence and the second block signal are transmitted atleast via a second antenna of the transmitter.
 13. The communicationapparatus according to claim 10, further comprising: an analog circuitcoupled to the receiving antenna, wherein the analog circuit converts,into baseband signals, signals of the first sequence, the secondsequence, the first block signal, and the second block signal receivedvia the receiving antenna, and outputs the baseband signals to thereceiver.
 14. A transmission method for use in a transmitter fortransmitting signals via a first antenna and a second antenna,comprising: generating a first sequence, a second sequence, a firstblock signal, and a second block signal, the first sequence being thesame as a sequence obtained by performing a first cyclic shift on aCAZAC sequence, an amount of the first cyclic shift being a firstamount, the second sequence being the same as a sequence obtained byperforming a second cyclic shift on the CAZAC sequence, an amount of thesecond cyclic shift being a second amount different from the firstamount, the first block signal being the same as a signal obtained byperforming a third cyclic shift on a block signal, an amount of thethird cyclic shift being a third amount, the second block signal beingthe same as a signal obtained by performing a fourth cyclic shift on theblock signal, an amount of the fourth cyclic shift being a fourth amountdifferent from the third amount; wherein a period in which the firstsequence and the second sequence are transmitted differs from a periodin which the first block signal and the second block signal aretransmitted; a gap between the first amount and the second amountdiffers from a gap between the third amount and the fourth amount; thefirst sequence and the first block signal are transmitted at least via afirst antenna; and the second sequence and the second block signal aretransmitted at least via a second antenna.
 15. The transmission methodaccording to claim 14, wherein a frequency with which the first blocksignal and the second block signal are transmitted is set for thetransmitter;
 16. A receiving method for use in a receiver for receivingsignals from a transmitter, comprising: receiving a first sequence, asecond sequence, a first block signal, and a second block signal, thefirst sequence being the same as a sequence obtained by performing afirst cyclic shift on a CAZAC sequence, an amount of the first cyclicshift being a first amount, the second sequence being the same as asequence obtained by performing a second cyclic shift on the CAZACsequence, an amount of the second cyclic shift being a second amountdifferent from the first amount, the first block signal being the sameas a signal obtained by performing a third cyclic shift on a blocksignal, an amount of the third cyclic shift being a third amount, thesecond block signal being the same as a signal obtained by performing afourth cyclic shift on the block signal, an amount of the fourth cyclicshift being a fourth amount different from the third amount, wherein thefirst sequence, the second sequence, the first block signal, and thesecond block signal are received via a receiving antenna; a period inwhich the first sequence and the second sequence are received differsfrom a period in which the first block signal and the second blocksignal are transmitted; and a gap between the first amount and thesecond amount differs from a gap between the third amount and the fourthamount.
 17. The receiving method according to claim 16, wherein afrequency with which the first block signal and the second block signalare received is set for the transmitter.